"The Lottery" is a short story written by Shirley Jackson. It was first published in 1948. It follows the story of a small town that holds a "lottery" every year on June 27th. When reading the story, the reader realizes that this "lottery" is all but harmless and that something very sinister is going on.
At the beginning of the story, the author indicates that the annual ritual of the "lottery" does not only take place in this one town, but in other towns in the area, too. We can see that in the author's choice of using the expression "in some towns." As you point out in your question, however, we find out that the "lottery" is done quicker in some areas than in others: "in some towns there were so many people that the lottery took two days."
In order to help you answer your question, it is first of all important to explain what this "lottery" actually is: the "lottery" involves heads of families drawing a slip of paper. If this slip of paper contains a black dot, this means that a member of this family will be stoned to death. This is the reason why the fact that this ritual can take place much quicker in this town is significant: as there are fewer people living here, this means that the probability of a family's name being chosen is much higher compared to a bigger town with more families. As a result, people in this town would be a lot more anxious when it comes to drawing their slip of paper. The reader also experiences this increased anxiety and tension when reading the story.